In Churchill, Manitoba, a tiny town in the farthest of far away areas in northern Canada, things are a little different. Polar bears and beluga whales are tourism staples. Snowmobiles are often the ride of choice. There are roads in Churchill, of course, but there are no roads to Churchill. Or from it. You have to fly in and out, or take a train, or a boat across the vast Hudson Bay.
For scientists, though, this area is unique for a wholly different reason.
It's the gravity — as in Sir Isaac Newton and gravity.
In places in and around Canada's Hudson Bay, the gravity is slightly off. In fact, it's quite a bit less than it is in much of the rest of the world.
It's nothing you would notice. Nobody in Churchill is bouncing around Buzz Aldrin-style. The lesser gravitational pull works out to about a 10th of an ounce for every 150 pounds of weight. If you're a 300-pounder, a fifth of an ounce really isn't going to make a difference.
Still, scientifically speaking, this matters. Scientists build careers making note of these types of things.
Gravity is always in flux
For years, researchers have guessed something was a out of whack with the gravity in Hudson Bay, based on two basic scientific principles:
First, gravity is proportional to mass. In other words, the bigger an object, the more pull it has. This is Sir Isaac 101.
Second, the Hudson Bay is the epicenter for what used to be one of the largest glaciers in the world. So the geographical lay of the Hudson Bay area — its mass, if you will — has changed a great deal in the past 20,000 years or so, and that isn't all that unusual. "If the Earth were a perfect sphere, gravity would be the same everywhere around the sphere," Mark Tamisiea of the Harvard-Smithsonian Center for Astrophysics told LiveScience.
A few years ago, scientists set out to show that in places where the mass of the Earth seemed lesser, the gravity would be lighter. Hudson Bay was a natural place to test the theory. Tamisiea and others crunched data from a pair of NASA satellites launched in 2007 to prove their point.
NASA's GRACE (Gravity Recovery and Climate Experiment) satellites measure, to a remarkable degree of accuracy, changes in the Earth's surface to determine how those changes may affect, among other things, the climate. Last year, for example, the satellites measured that Brazil lost an estimated 15 trillion gallons of water per year from 2012-2015.
The two satellites, which travel a set distance apart, are pulled at different rates as they pass over different parts of the Earth. The two satellites then extrapolate how much different the surface is — and the gravitational pull of it — by measuring how much the distance between them changes. They found what scientists call a gravitational anomaly in Hudson Bay.
Where'd the gravity go?
The reasons for the anomaly are disputed. Many think that it has to do with glaciers, at least in part.
One thought is that as the Laurentide ice sheet, a massive glacier, retreated thousands of years ago, the land under the ice remained depressed from its weight. (These glaciers were miles thick at certain points.) That retreat formed two large domes to the east and west of Hudson Bay.
Once the heavy glacier pulled back, the lighter mass led to less gravity. And even though the land is bouncing back, according to scientists, it will be many thousands of years until the mass and the accompanying gravity are back where they should be.
"We are able to show that the ghost of the ice age still hangs over North America," Jerry Mitrovica, a physicist at the University of Toronto, told LiveScience in 2007.
Another theory, which could work in conjunction with the glacier idea, is that rock underneath the area, in the planet's mantle, is slowly being pulled downward to the core, altering mass and gravity.
The difference in gravity between Hudson Bay and other parts of the world raises other questions, too, based on the relationship between gravity (or lack of it) and time. This is more Einstein than Newton, and it's all relative.
Whatever the case, Hudson Bay and its sparsely populated towns — Churchill is one of the biggest, yet fewer than 1,000 people live there — remains a unique place in the world. The bears. The whales. The snow and ice and the northern lights. It has, you might say, an attraction all its own.